Extended Type I glycosphingolipid is a cell surface molecule that can be associated with, for example, certain malignant states.
Aberrant glycosylation has been observed to be a common feature of many cancer types, Hakomori, PNAS 99:10231-10233, 2002. Some of the carbohydrate antigens used for the diagnosis of human cancers carry polylactosamine structures. Polylactosamines are usually classified into two categories according to the unit structure. A polylactosamine having the Galβ1→3GlcNAc structure is called a Type I chain, and that having the Galβ1→4GlcNAc structure is referred to as a Type II chain. The most common tumor-associated antigens found in some human cancers have the lacto series Type II chain structure, which usually is sialylated and/or fucosylated. Type I chain antigens are abundant in normal cells and tissues, and occasionally are associated with cancer, Stroud et al., JBC 266: 8439-8446, 1991. For example, 2→3 sialylated Lea antigen (the CA 19-9 antigen defined by the N19-9 antibody) is a cancer-associated Type I chain antigen. However, cancer diagnostic methods based on the detection of those Type I antigens have been hampered by high false positive and/or high false negative incidences, see, for example U.S. Pat. Nos. 6,083,929 and 6,294,523.
Two mouse monoclonal antibodies, NCC-ST421 and IMH2, were raised against extended Type I chain antigens. NCC-ST421 is specific for Lea-Lea. The NCC-ST421 antibody strongly induced antibody dependant cell cytotoxicity (ADCC) using human peripheral blood leukocytes as effectors against a variety of human tumor cells, and induced complement dependent cytotoxicity (CDC) with a human complement source, Watanabe et al., Cancer Res. 51:2199-2204, 1991. The Lea-Lea antigen was found to be highly expressed in the human colon carcinoma cell line, Colo205.
IMH2 was also established against extended Type I chains. IMH2 bound to Leb-Lea, Ley-Lex, Leb and Ley based on 1H-NMR, FAB-MS and enzymatic degradation studies, Stroud et al., Eur. J. Biochem. 203:577-586, 1992. IMH2 showed strong lymphocyte-activated, as well as, complement-dependent killing of Colo205 cells in vitro, and inhibited Colo205 growth in vivo.
IMH2 reacted with carcinoma tissues derived from colon, pancreas, liver and endometrium. However, normal colon showed no reactivity with IMH2. Normal liver and pancreas showed weak or highly restricted reactivity in normal hepatocytes and islets of Langerhans cells. Immunochemical staining intensity was much stronger in endometrial carcinomas than in normal endometrium, Ito et al., Cancer Res. 52:3739-3745, 1992.
Both NCC-ST421 and IMH2 exhibit inhibition of tumor growth in nude mice after inoculation of human tumor cells expressing the extended Type I chain antigen, but no inhibition of growth occurred in tumor cells that did not express extended Type I chain antigen.
Because of the abundance of Type I structures on normal cells, the use of Type I antibodies for diagnostic and/or therapeutic purposes heretofore was not possible.
Conventional cancer treatments, such as chemotherapy and radiotherapy, have shown some advantages in various cancer patients. Despite the benefits of antitumor activity in conventional therapies, however, treatment-induced toxicity to normal tissues can substantially reduce the quality of life in cancer patients. Dose intensification for better antitumor activity is also limited. Monoclonal antibodies enable the promise of targeted cytotoxicity, focusing on tumor tissues, but not normal tissues.
Monoclonal antibodies (mAbs) can be developed with high specificity for antigens expressed on tumor cells and can elicit desired antitumor activities. The promise of mAbs was furthered by the development of mice that produce fully human mAbs. One such tool is the KM mouse, U.S. Pat. No. 7,041,870 and Tomizuka et al., Nat. Genet. 16:133-143, 1997. In the KM mouse, the mouse genes encoding immunoglobulins were inactivated and replaced with human antibody genes. Thus, the KM mouse expresses fully human antibodies.
Several fully human antibodies have been successfully developed using the KM mouse.
For example, Motoki et al. developed a human IgG (KMTR2) which directed antibody dependent oligomerization of TRAIL-R2 and initiated efficient apoptotic signaling and tumor regression independent of host effector function (Clin. Cancer Res. 11(8):3126-3135, 2005; and see U.S. Pat. No. 7,115,717 and Imakire et al., Int. J. Cancer 108:564-570, 2004). HD8, a fully human monoclonal antibody specific for human leukocyte antigen DR (HLA-DR), exerted antibody-dependent cellular cytotoxicity (ADCC) as well as complement-dependent cytotoxicity (CDC) in vitro, and extended the life span of immunocompromised mice inoculated with non-Hodgkin lymphoma cell lines, Tawara et al., Cancer Sci. 98 (6) 921-928, 2007.
Additionally, two human IgMs raised in KM mice and directed to carbohydrate antigens were reported. HMMC-1 specifically recognizes a novel O-glycan structure, reacts positively with Mullerian duct-related carcinomas, and exhibits complement dependent cytotoxicity on a human uterine endometrial cancer cell line, SNG-S, Nozawa et al., Clin Cancer. Res. 10:7071-7078, 2004. Another human monoclonal IgM, HMOCC-1, recognizing a glycoprotein located on the cell membrane, reacted with ovarian cancer (Suzuki et al., Gynecol. Oncol. 95:290-298, 2004). Since those two antibodies are IgMs, the application of those antibodies in cancer therapy should be limited by molecule size and restrictions in production.